params.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Helpers for initial module or kernel cmdline parsing
 * Copyright (C) 2001 Rusty Russell.
 */
#include <linux/ctype.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/kstrtox.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/overflow.h>
#include <linux/security.h>
#include <linux/slab.h>
#include <linux/string.h>

#ifdef CONFIG_SYSFS
/* Protects all built-in parameters, modules use their own param_lock */
static DEFINE_MUTEX(param_lock);

/* Use the module's mutex, or if built-in use the built-in mutex */
#ifdef CONFIG_MODULES
#define KPARAM_MUTEX(mod)	((mod) ? &(mod)->param_lock : &param_lock)
#else
#define KPARAM_MUTEX(mod)	(&param_lock)
#endif

static inline void check_kparam_locked(struct module *mod)
{
	BUG_ON(!mutex_is_locked(KPARAM_MUTEX(mod)));
}
#else
static inline void check_kparam_locked(struct module *mod)
{
}
#endif /* !CONFIG_SYSFS */

/* This just allows us to keep track of which parameters are kmalloced. */
struct kmalloced_param {
	struct list_head list;
	char val[];
};
static LIST_HEAD(kmalloced_params);
static DEFINE_SPINLOCK(kmalloced_params_lock);

static void *kmalloc_parameter(unsigned int size)
{
	struct kmalloced_param *p;

	p = kmalloc(size_add(sizeof(*p), size), GFP_KERNEL);
	if (!p)
		return NULL;

	spin_lock(&kmalloced_params_lock);
	list_add(&p->list, &kmalloced_params);
	spin_unlock(&kmalloced_params_lock);

	return p->val;
}

/* Does nothing if parameter wasn't kmalloced above. */
static void maybe_kfree_parameter(void *param)
{
	struct kmalloced_param *p;

	spin_lock(&kmalloced_params_lock);
	list_for_each_entry(p, &kmalloced_params, list) {
		if (p->val == param) {
			list_del(&p->list);
			kfree(p);
			break;
		}
	}
	spin_unlock(&kmalloced_params_lock);
}

static char dash2underscore(char c)
{
	if (c == '-')
		return '_';
	return c;
}

bool parameqn(const char *a, const char *b, size_t n)
{
	size_t i;

	for (i = 0; i < n; i++) {
		if (dash2underscore(a[i]) != dash2underscore(b[i]))
			return false;
	}
	return true;
}

bool parameq(const char *a, const char *b)
{
	return parameqn(a, b, strlen(a)+1);
}

static bool param_check_unsafe(const struct kernel_param *kp)
{
	if (kp->flags & KERNEL_PARAM_FL_HWPARAM &&
	    security_locked_down(LOCKDOWN_MODULE_PARAMETERS))
		return false;

	if (kp->flags & KERNEL_PARAM_FL_UNSAFE) {
		pr_notice("Setting dangerous option %s - tainting kernel\n",
			  kp->name);
		add_taint(TAINT_USER, LOCKDEP_STILL_OK);
	}

	return true;
}

static int parse_one(char *param,
		     char *val,
		     const char *doing,
		     const struct kernel_param *params,
		     unsigned num_params,
		     s16 min_level,
		     s16 max_level,
		     void *arg, parse_unknown_fn handle_unknown)
{
	unsigned int i;
	int err;

	/* Find parameter */
	for (i = 0; i < num_params; i++) {
		if (parameq(param, params[i].name)) {
			if (params[i].level < min_level
			    || params[i].level > max_level)
				return 0;
			/* No one handled NULL, so do it here. */
			if (!val &&
			    !(params[i].ops->flags & KERNEL_PARAM_OPS_FL_NOARG))
				return -EINVAL;
			pr_debug("handling %s with %p\n", param,
				params[i].ops->set);
			kernel_param_lock(params[i].mod);
			if (param_check_unsafe(&params[i]))
				err = params[i].ops->set(val, &params[i]);
			else
				err = -EPERM;
			kernel_param_unlock(params[i].mod);
			return err;
		}
	}

	if (handle_unknown) {
		pr_debug("doing %s: %s='%s'\n", doing, param, val);
		return handle_unknown(param, val, doing, arg);
	}

	pr_debug("Unknown argument '%s'\n", param);
	return -ENOENT;
}

/* Args looks like "foo=bar,bar2 baz=fuz wiz". */
char *parse_args(const char *doing,
		 char *args,
		 const struct kernel_param *params,
		 unsigned num,
		 s16 min_level,
		 s16 max_level,
		 void *arg, parse_unknown_fn unknown)
{
	char *param, *val, *err = NULL;

	/* Chew leading spaces */
	args = skip_spaces(args);

	if (*args)
		pr_debug("doing %s, parsing ARGS: '%s'\n", doing, args);

	while (*args) {
		int ret;
		int irq_was_disabled;

		args = next_arg(args, &param, &val);
		/* Stop at -- */
		if (!val && strcmp(param, "--") == 0)
			return err ?: args;
		irq_was_disabled = irqs_disabled();
		ret = parse_one(param, val, doing, params, num,
				min_level, max_level, arg, unknown);
		if (irq_was_disabled && !irqs_disabled())
			pr_warn("%s: option '%s' enabled irq's!\n",
				doing, param);

		switch (ret) {
		case 0:
			continue;
		case -ENOENT:
			pr_err("%s: Unknown parameter `%s'\n", doing, param);
			break;
		case -ENOSPC:
			pr_err("%s: `%s' too large for parameter `%s'\n",
			       doing, val ?: "", param);
			break;
		default:
			pr_err("%s: `%s' invalid for parameter `%s'\n",
			       doing, val ?: "", param);
			break;
		}

		err = ERR_PTR(ret);
	}

	return err;
}

/* Lazy bastard, eh? */
#define STANDARD_PARAM_DEF(name, type, format, strtolfn)      		\
	int param_set_##name(const char *val, const struct kernel_param *kp) \
	{								\
		return strtolfn(val, 0, (type *)kp->arg);		\
	}								\
	int param_get_##name(char *buffer, const struct kernel_param *kp) \
	{								\
		return scnprintf(buffer, PAGE_SIZE, format "\n",	\
				*((type *)kp->arg));			\
	}								\
	const struct kernel_param_ops param_ops_##name = {			\
		.set = param_set_##name,				\
		.get = param_get_##name,				\
	};								\
	EXPORT_SYMBOL(param_set_##name);				\
	EXPORT_SYMBOL(param_get_##name);				\
	EXPORT_SYMBOL(param_ops_##name)


STANDARD_PARAM_DEF(byte,	unsigned char,		"%hhu",		kstrtou8);
STANDARD_PARAM_DEF(short,	short,			"%hi",		kstrtos16);
STANDARD_PARAM_DEF(ushort,	unsigned short,		"%hu",		kstrtou16);
STANDARD_PARAM_DEF(int,		int,			"%i",		kstrtoint);
STANDARD_PARAM_DEF(uint,	unsigned int,		"%u",		kstrtouint);
STANDARD_PARAM_DEF(long,	long,			"%li",		kstrtol);
STANDARD_PARAM_DEF(ulong,	unsigned long,		"%lu",		kstrtoul);
STANDARD_PARAM_DEF(ullong,	unsigned long long,	"%llu",		kstrtoull);
STANDARD_PARAM_DEF(hexint,	unsigned int,		"%#08x", 	kstrtouint);

int param_set_uint_minmax(const char *val, const struct kernel_param *kp,
		unsigned int min, unsigned int max)
{
	unsigned int num;
	int ret;

	if (!val)
		return -EINVAL;
	ret = kstrtouint(val, 0, &num);
	if (ret)
		return ret;
	if (num < min || num > max)
		return -EINVAL;
	*((unsigned int *)kp->arg) = num;
	return 0;
}
EXPORT_SYMBOL_GPL(param_set_uint_minmax);

int param_set_charp(const char *val, const struct kernel_param *kp)
{
	size_t len, maxlen = 1024;

	len = strnlen(val, maxlen + 1);
	if (len == maxlen + 1) {
		pr_err("%s: string parameter too long\n", kp->name);
		return -ENOSPC;
	}

	maybe_kfree_parameter(*(char **)kp->arg);

	/*
	 * This is a hack. We can't kmalloc() in early boot, and we
	 * don't need to; this mangled commandline is preserved.
	 */
	if (slab_is_available()) {
		*(char **)kp->arg = kmalloc_parameter(len + 1);
		if (!*(char **)kp->arg)
			return -ENOMEM;
		strcpy(*(char **)kp->arg, val);
	} else
		*(const char **)kp->arg = val;

	return 0;
}
EXPORT_SYMBOL(param_set_charp);

int param_get_charp(char *buffer, const struct kernel_param *kp)
{
	return scnprintf(buffer, PAGE_SIZE, "%s\n", *((char **)kp->arg));
}
EXPORT_SYMBOL(param_get_charp);

void param_free_charp(void *arg)
{
	maybe_kfree_parameter(*((char **)arg));
}
EXPORT_SYMBOL(param_free_charp);

const struct kernel_param_ops param_ops_charp = {
	.set = param_set_charp,
	.get = param_get_charp,
	.free = param_free_charp,
};
EXPORT_SYMBOL(param_ops_charp);

/* Actually could be a bool or an int, for historical reasons. */
int param_set_bool(const char *val, const struct kernel_param *kp)
{
	/* No equals means "set"... */
	if (!val) val = "1";

	/* One of =[yYnN01] */
	return kstrtobool(val, kp->arg);
}
EXPORT_SYMBOL(param_set_bool);

int param_get_bool(char *buffer, const struct kernel_param *kp)
{
	/* Y and N chosen as being relatively non-coder friendly */
	return sprintf(buffer, "%c\n", *(bool *)kp->arg ? 'Y' : 'N');
}
EXPORT_SYMBOL(param_get_bool);

const struct kernel_param_ops param_ops_bool = {
	.flags = KERNEL_PARAM_OPS_FL_NOARG,
	.set = param_set_bool,
	.get = param_get_bool,
};
EXPORT_SYMBOL(param_ops_bool);

int param_set_bool_enable_only(const char *val, const struct kernel_param *kp)
{
	int err;
	bool new_value;
	bool orig_value = *(bool *)kp->arg;
	struct kernel_param dummy_kp = *kp;

	dummy_kp.arg = &new_value;

	err = param_set_bool(val, &dummy_kp);
	if (err)
		return err;

	/* Don't let them unset it once it's set! */
	if (!new_value && orig_value)
		return -EROFS;

	if (new_value)
		err = param_set_bool(val, kp);

	return err;
}
EXPORT_SYMBOL_GPL(param_set_bool_enable_only);

const struct kernel_param_ops param_ops_bool_enable_only = {
	.flags = KERNEL_PARAM_OPS_FL_NOARG,
	.set = param_set_bool_enable_only,
	.get = param_get_bool,
};
EXPORT_SYMBOL_GPL(param_ops_bool_enable_only);

/* This one must be bool. */
int param_set_invbool(const char *val, const struct kernel_param *kp)
{
	int ret;
	bool boolval;
	struct kernel_param dummy;

	dummy.arg = &boolval;
	ret = param_set_bool(val, &dummy);
	if (ret == 0)
		*(bool *)kp->arg = !boolval;
	return ret;
}
EXPORT_SYMBOL(param_set_invbool);

int param_get_invbool(char *buffer, const struct kernel_param *kp)
{
	return sprintf(buffer, "%c\n", (*(bool *)kp->arg) ? 'N' : 'Y');
}
EXPORT_SYMBOL(param_get_invbool);

const struct kernel_param_ops param_ops_invbool = {
	.set = param_set_invbool,
	.get = param_get_invbool,
};
EXPORT_SYMBOL(param_ops_invbool);

int param_set_bint(const char *val, const struct kernel_param *kp)
{
	/* Match bool exactly, by re-using it. */
	struct kernel_param boolkp = *kp;
	bool v;
	int ret;

	boolkp.arg = &v;

	ret = param_set_bool(val, &boolkp);
	if (ret == 0)
		*(int *)kp->arg = v;
	return ret;
}
EXPORT_SYMBOL(param_set_bint);

const struct kernel_param_ops param_ops_bint = {
	.flags = KERNEL_PARAM_OPS_FL_NOARG,
	.set = param_set_bint,
	.get = param_get_int,
};
EXPORT_SYMBOL(param_ops_bint);

/* We break the rule and mangle the string. */
static int param_array(struct module *mod,
		       const char *name,
		       const char *val,
		       unsigned int min, unsigned int max,
		       void *elem, int elemsize,
		       int (*set)(const char *, const struct kernel_param *kp),
		       s16 level,
		       unsigned int *num)
{
	int ret;
	struct kernel_param kp;
	char save;

	/* Get the name right for errors. */
	kp.name = name;
	kp.arg = elem;
	kp.level = level;

	*num = 0;
	/* We expect a comma-separated list of values. */
	do {
		int len;

		if (*num == max) {
			pr_err("%s: can only take %i arguments\n", name, max);
			return -EINVAL;
		}
		len = strcspn(val, ",");

		/* nul-terminate and parse */
		save = val[len];
		((char *)val)[len] = '\0';
		check_kparam_locked(mod);
		ret = set(val, &kp);

		if (ret != 0)
			return ret;
		kp.arg += elemsize;
		val += len+1;
		(*num)++;
	} while (save == ',');

	if (*num < min) {
		pr_err("%s: needs at least %i arguments\n", name, min);
		return -EINVAL;
	}
	return 0;
}

static int param_array_set(const char *val, const struct kernel_param *kp)
{
	const struct kparam_array *arr = kp->arr;
	unsigned int temp_num;

	return param_array(kp->mod, kp->name, val, 1, arr->max, arr->elem,
			   arr->elemsize, arr->ops->set, kp->level,
			   arr->num ?: &temp_num);
}

static int param_array_get(char *buffer, const struct kernel_param *kp)
{
	int i, off, ret;
	const struct kparam_array *arr = kp->arr;
	struct kernel_param p = *kp;

	for (i = off = 0; i < (arr->num ? *arr->num : arr->max); i++) {
		/* Replace \n with comma */
		if (i)
			buffer[off - 1] = ',';
		p.arg = arr->elem + arr->elemsize * i;
		check_kparam_locked(p.mod);
		ret = arr->ops->get(buffer + off, &p);
		if (ret < 0)
			return ret;
		off += ret;
	}
	buffer[off] = '\0';
	return off;
}

static void param_array_free(void *arg)
{
	unsigned int i;
	const struct kparam_array *arr = arg;

	if (arr->ops->free)
		for (i = 0; i < (arr->num ? *arr->num : arr->max); i++)
			arr->ops->free(arr->elem + arr->elemsize * i);
}

const struct kernel_param_ops param_array_ops = {
	.set = param_array_set,
	.get = param_array_get,
	.free = param_array_free,
};
EXPORT_SYMBOL(param_array_ops);

int param_set_copystring(const char *val, const struct kernel_param *kp)
{
	const struct kparam_string *kps = kp->str;

	if (strnlen(val, kps->maxlen) == kps->maxlen) {
		pr_err("%s: string doesn't fit in %u chars.\n",
		       kp->name, kps->maxlen-1);
		return -ENOSPC;
	}
	strcpy(kps->string, val);
	return 0;
}
EXPORT_SYMBOL(param_set_copystring);

int param_get_string(char *buffer, const struct kernel_param *kp)
{
	const struct kparam_string *kps = kp->str;
	return scnprintf(buffer, PAGE_SIZE, "%s\n", kps->string);
}
EXPORT_SYMBOL(param_get_string);

const struct kernel_param_ops param_ops_string = {
	.set = param_set_copystring,
	.get = param_get_string,
};
EXPORT_SYMBOL(param_ops_string);

/* sysfs output in /sys/modules/XYZ/parameters/ */
#define to_module_attr(n) container_of_const(n, struct module_attribute, attr)
#define to_module_kobject(n) container_of(n, struct module_kobject, kobj)

struct param_attribute
{
	struct module_attribute mattr;
	const struct kernel_param *param;
};

struct module_param_attrs
{
	unsigned int num;
	struct attribute_group grp;
	struct param_attribute attrs[] __counted_by(num);
};

#ifdef CONFIG_SYSFS
#define to_param_attr(n) container_of_const(n, struct param_attribute, mattr)

static ssize_t param_attr_show(const struct module_attribute *mattr,
			       struct module_kobject *mk, char *buf)
{
	int count;
	const struct param_attribute *attribute = to_param_attr(mattr);

	if (!attribute->param->ops->get)
		return -EPERM;

	kernel_param_lock(mk->mod);
	count = attribute->param->ops->get(buf, attribute->param);
	kernel_param_unlock(mk->mod);
	return count;
}

/* sysfs always hands a nul-terminated string in buf.  We rely on that. */
static ssize_t param_attr_store(const struct module_attribute *mattr,
				struct module_kobject *mk,
				const char *buf, size_t len)
{
 	int err;
	const struct param_attribute *attribute = to_param_attr(mattr);

	if (!attribute->param->ops->set)
		return -EPERM;

	kernel_param_lock(mk->mod);
	if (param_check_unsafe(attribute->param))
		err = attribute->param->ops->set(buf, attribute->param);
	else
		err = -EPERM;
	kernel_param_unlock(mk->mod);
	if (!err)
		return len;
	return err;
}
#endif

#ifdef CONFIG_MODULES
#define __modinit
#else
#define __modinit __init
#endif

#ifdef CONFIG_SYSFS
void kernel_param_lock(struct module *mod)
{
	mutex_lock(KPARAM_MUTEX(mod));
}

void kernel_param_unlock(struct module *mod)
{
	mutex_unlock(KPARAM_MUTEX(mod));
}

EXPORT_SYMBOL(kernel_param_lock);
EXPORT_SYMBOL(kernel_param_unlock);

/*
 * add_sysfs_param - add a parameter to sysfs
 * @mk: struct module_kobject
 * @kp: the actual parameter definition to add to sysfs
 * @name: name of parameter
 *
 * Create a kobject if for a (per-module) parameter if mp NULL, and
 * create file in sysfs.  Returns an error on out of memory.  Always cleans up
 * if there's an error.
 */
static __modinit int add_sysfs_param(struct module_kobject *mk,
				     const struct kernel_param *kp,
				     const char *name)
{
	struct module_param_attrs *new_mp;
	struct attribute **new_attrs;
	unsigned int i;

	/* We don't bother calling this with invisible parameters. */
	BUG_ON(!kp->perm);

	if (!mk->mp) {
		/* First allocation. */
		mk->mp = kzalloc(sizeof(*mk->mp), GFP_KERNEL);
		if (!mk->mp)
			return -ENOMEM;
		mk->mp->grp.name = "parameters";
		/* NULL-terminated attribute array. */
		mk->mp->grp.attrs = kzalloc(sizeof(mk->mp->grp.attrs[0]),
					    GFP_KERNEL);
		/* Caller will cleanup via free_module_param_attrs */
		if (!mk->mp->grp.attrs)
			return -ENOMEM;
	}

	/* Enlarge allocations. */
	new_mp = krealloc(mk->mp, struct_size(mk->mp, attrs, mk->mp->num + 1),
			  GFP_KERNEL);
	if (!new_mp)
		return -ENOMEM;
	mk->mp = new_mp;
	mk->mp->num++;

	/* Extra pointer for NULL terminator */
	new_attrs = krealloc_array(mk->mp->grp.attrs, mk->mp->num + 1,
				   sizeof(mk->mp->grp.attrs[0]), GFP_KERNEL);
	if (!new_attrs)
		return -ENOMEM;
	mk->mp->grp.attrs = new_attrs;

	/* Tack new one on the end. */
	memset(&mk->mp->attrs[mk->mp->num - 1], 0, sizeof(mk->mp->attrs[0]));
	sysfs_attr_init(&mk->mp->attrs[mk->mp->num - 1].mattr.attr);
	mk->mp->attrs[mk->mp->num - 1].param = kp;
	mk->mp->attrs[mk->mp->num - 1].mattr.show = param_attr_show;
	/* Do not allow runtime DAC changes to make param writable. */
	if ((kp->perm & (S_IWUSR | S_IWGRP | S_IWOTH)) != 0)
		mk->mp->attrs[mk->mp->num - 1].mattr.store = param_attr_store;
	else
		mk->mp->attrs[mk->mp->num - 1].mattr.store = NULL;
	mk->mp->attrs[mk->mp->num - 1].mattr.attr.name = (char *)name;
	mk->mp->attrs[mk->mp->num - 1].mattr.attr.mode = kp->perm;

	/* Fix up all the pointers, since krealloc can move us */
	for (i = 0; i < mk->mp->num; i++)
		mk->mp->grp.attrs[i] = &mk->mp->attrs[i].mattr.attr;
	mk->mp->grp.attrs[mk->mp->num] = NULL;
	return 0;
}

#ifdef CONFIG_MODULES
static void free_module_param_attrs(struct module_kobject *mk)
{
	if (mk->mp)
		kfree(mk->mp->grp.attrs);
	kfree(mk->mp);
	mk->mp = NULL;
}

/*
 * module_param_sysfs_setup - setup sysfs support for one module
 * @mod: module
 * @kparam: module parameters (array)
 * @num_params: number of module parameters
 *
 * Adds sysfs entries for module parameters under
 * /sys/module/[mod->name]/parameters/
 */
int module_param_sysfs_setup(struct module *mod,
			     const struct kernel_param *kparam,
			     unsigned int num_params)
{
	int i, err;
	bool params = false;

	for (i = 0; i < num_params; i++) {
		if (kparam[i].perm == 0)
			continue;
		err = add_sysfs_param(&mod->mkobj, &kparam[i], kparam[i].name);
		if (err) {
			free_module_param_attrs(&mod->mkobj);
			return err;
		}
		params = true;
	}

	if (!params)
		return 0;

	/* Create the param group. */
	err = sysfs_create_group(&mod->mkobj.kobj, &mod->mkobj.mp->grp);
	if (err)
		free_module_param_attrs(&mod->mkobj);
	return err;
}

/*
 * module_param_sysfs_remove - remove sysfs support for one module
 * @mod: module
 *
 * Remove sysfs entries for module parameters and the corresponding
 * kobject.
 */
void module_param_sysfs_remove(struct module *mod)
{
	if (mod->mkobj.mp) {
		sysfs_remove_group(&mod->mkobj.kobj, &mod->mkobj.mp->grp);
		/*
		 * We are positive that no one is using any param
		 * attrs at this point. Deallocate immediately.
		 */
		free_module_param_attrs(&mod->mkobj);
	}
}
#endif

void destroy_params(const struct kernel_param *params, unsigned num)
{
	unsigned int i;

	for (i = 0; i < num; i++)
		if (params[i].ops->free)
			params[i].ops->free(params[i].arg);
}

static struct module_kobject * __init locate_module_kobject(const char *name)
{
	struct module_kobject *mk;
	struct kobject *kobj;
	int err;

	kobj = kset_find_obj(module_kset, name);
	if (kobj) {
		mk = to_module_kobject(kobj);
	} else {
		mk = kzalloc(sizeof(struct module_kobject), GFP_KERNEL);
		BUG_ON(!mk);

		mk->mod = THIS_MODULE;
		mk->kobj.kset = module_kset;
		err = kobject_init_and_add(&mk->kobj, &module_ktype, NULL,
					   "%s", name);
#ifdef CONFIG_MODULES
		if (!err)
			err = sysfs_create_file(&mk->kobj, &module_uevent.attr);
#endif
		if (err) {
			kobject_put(&mk->kobj);
			pr_crit("Adding module '%s' to sysfs failed (%d), the system may be unstable.\n",
				name, err);
			return NULL;
		}

		/* So that we hold reference in both cases. */
		kobject_get(&mk->kobj);
	}

	return mk;
}

static void __init kernel_add_sysfs_param(const char *name,
					  const struct kernel_param *kparam,
					  unsigned int name_skip)
{
	struct module_kobject *mk;
	int err;

	mk = locate_module_kobject(name);
	if (!mk)
		return;

	/* We need to remove old parameters before adding more. */
	if (mk->mp)
		sysfs_remove_group(&mk->kobj, &mk->mp->grp);

	/* These should not fail at boot. */
	err = add_sysfs_param(mk, kparam, kparam->name + name_skip);
	BUG_ON(err);
	err = sysfs_create_group(&mk->kobj, &mk->mp->grp);
	BUG_ON(err);
	kobject_uevent(&mk->kobj, KOBJ_ADD);
	kobject_put(&mk->kobj);
}

/*
 * param_sysfs_builtin - add sysfs parameters for built-in modules
 *
 * Add module_parameters to sysfs for "modules" built into the kernel.
 *
 * The "module" name (KBUILD_MODNAME) is stored before a dot, the
 * "parameter" name is stored behind a dot in kernel_param->name. So,
 * extract the "module" name for all built-in kernel_param-eters,
 * and for all who have the same, call kernel_add_sysfs_param.
 */
static void __init param_sysfs_builtin(void)
{
	const struct kernel_param *kp;
	unsigned int name_len;
	char modname[MODULE_NAME_LEN];

	for (kp = __start___param; kp < __stop___param; kp++) {
		char *dot;

		if (kp->perm == 0)
			continue;

		dot = strchr(kp->name, '.');
		if (!dot) {
			/* This happens for core_param() */
			strcpy(modname, "kernel");
			name_len = 0;
		} else {
			name_len = dot - kp->name + 1;
			strscpy(modname, kp->name, name_len);
		}
		kernel_add_sysfs_param(modname, kp, name_len);
	}
}

ssize_t __modver_version_show(const struct module_attribute *mattr,
			      struct module_kobject *mk, char *buf)
{
	const struct module_version_attribute *vattr =
		container_of_const(mattr, struct module_version_attribute, mattr);

	return scnprintf(buf, PAGE_SIZE, "%s\n", vattr->version);
}

extern const struct module_version_attribute __start___modver[];
extern const struct module_version_attribute __stop___modver[];

static void __init version_sysfs_builtin(void)
{
	const struct module_version_attribute *vattr;
	struct module_kobject *mk;
	int err;

	for (vattr = __start___modver; vattr < __stop___modver; vattr++) {
		mk = locate_module_kobject(vattr->module_name);
		if (mk) {
			err = sysfs_create_file(&mk->kobj, &vattr->mattr.attr);
			WARN_ON_ONCE(err);
			kobject_uevent(&mk->kobj, KOBJ_ADD);
			kobject_put(&mk->kobj);
		}
	}
}

/* module-related sysfs stuff */

static ssize_t module_attr_show(struct kobject *kobj,
				struct attribute *attr,
				char *buf)
{
	const struct module_attribute *attribute;
	struct module_kobject *mk;
	int ret;

	attribute = to_module_attr(attr);
	mk = to_module_kobject(kobj);

	if (!attribute->show)
		return -EIO;

	ret = attribute->show(attribute, mk, buf);

	return ret;
}

static ssize_t module_attr_store(struct kobject *kobj,
				struct attribute *attr,
				const char *buf, size_t len)
{
	const struct module_attribute *attribute;
	struct module_kobject *mk;
	int ret;

	attribute = to_module_attr(attr);
	mk = to_module_kobject(kobj);

	if (!attribute->store)
		return -EIO;

	ret = attribute->store(attribute, mk, buf, len);

	return ret;
}

static const struct sysfs_ops module_sysfs_ops = {
	.show = module_attr_show,
	.store = module_attr_store,
};

static int uevent_filter(const struct kobject *kobj)
{
	const struct kobj_type *ktype = get_ktype(kobj);

	if (ktype == &module_ktype)
		return 1;
	return 0;
}

static const struct kset_uevent_ops module_uevent_ops = {
	.filter = uevent_filter,
};

struct kset *module_kset;

static void module_kobj_release(struct kobject *kobj)
{
	struct module_kobject *mk = to_module_kobject(kobj);
	complete(mk->kobj_completion);
}

const struct kobj_type module_ktype = {
	.release   =	module_kobj_release,
	.sysfs_ops =	&module_sysfs_ops,
};

/*
 * param_sysfs_init - create "module" kset
 *
 * This must be done before the initramfs is unpacked and
 * request_module() thus becomes possible, because otherwise the
 * module load would fail in mod_sysfs_init.
 */
static int __init param_sysfs_init(void)
{
	module_kset = kset_create_and_add("module", &module_uevent_ops, NULL);
	if (!module_kset) {
		printk(KERN_WARNING "%s (%d): error creating kset\n",
			__FILE__, __LINE__);
		return -ENOMEM;
	}

	return 0;
}
subsys_initcall(param_sysfs_init);

/*
 * param_sysfs_builtin_init - add sysfs version and parameter
 * attributes for built-in modules
 */
static int __init param_sysfs_builtin_init(void)
{
	if (!module_kset)
		return -ENOMEM;

	version_sysfs_builtin();
	param_sysfs_builtin();

	return 0;
}
late_initcall(param_sysfs_builtin_init);

#endif /* CONFIG_SYSFS */